The present invention is directed to an electrolysis device employing bipolar electrodes which can be used for achieving electrochemical reactions, particularly the electrolysis of a saline solution to obtain an oxidizing solution containing chlorinated compounds, preferably in the form of sodium hypochlorite. Such a solution, having the same range of use as a commercial sodium hypochlorite solution, can be used to chlorinate waters of any type, including waste water, at any stage in the treatment of such water. The oxidizing compounds present in such a solution are measured in "active chlorine equivalents".
Electrolysers utilizing various types of bipolar electrode assemblies are known and are used industrially to achieve various electrochemical reactions. Such known devices, when utilized to obtain a sodium hypochlorite solution from an alkaline metal electrolyte, such as sea water, brackish water, or a sodium chloride solution, result in electrolytic oxidizing and reducing reactions in the immediate vicinity of the electrodes and in chemical reactions between the electrodes. The active chlorine present in the oxidizing solution obtained is dissociated and is found mainly in the form of hypochlorous acid and hypochlorite ions, depending among other things on the pH and the temperature, with simultaneous production of hydrogen. When the electrolyte consists of sea water, the presence of calcium and magnesium salts gives rise to the formation at the cathode of a deposit making it less permeable to the flow of electrons, and periodically requiring acid washing or short-term current inversions.
To avoid such disadvantages, it would be worthwhile on the one hand to limit the concentration of hydrogen formed, as hydrogen is harmful to good maintenance of the electrodes, by eliminating hydrogen during the treatment, and on the other hand to operate at relatively high electrolyte circulation rates between the electrodes in order to reduce the deposits on the cathode and to space or eliminate washing or current inversion operations.
However, to obtain high conversion rates and thus to increase the concentration of active chlorine equivalent in the solution obtained, the current density can be increased. If it is desired to obtain low specific KwH per kg consumption of active chlorine equivalent produced, it is then necessary to employ low voltages, which can be achievied by a reduction of the space between the two electrodes.
Also, during the course of the electrolysis operation, the chemical composition of the electrolyte is modified, thereby necessitating different operating conditions such as speed of the electrolyte between the electrodes and current density.